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Accessory Dwelling Units (ADUs)

You will find information on this page about adding an accessory dwelling unit to a property. Every dwelling unit functions as a separate unit. They are commonly known as "mother-in-law apartments", "granny-flats" or studio apartments.

An accessory dwelling unit (ADU) is a second dwelling unit created on a lot with a house, attached house or manufactured home. The second unit is created auxiliary to, and is smaller than, the main dwelling. ADUs can be created in a variety of ways, including conversion of a portion of an existing house, addition to an existing house, conversion of an existing garage or the construction of an entirely new building.

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A building permit is required to build an accessory dwelling unit. Depending on the scope of work, your project will most likely also require electrical, plumbing and/or mechanical permits. For new construction, your permit will be reviewed under provisions of the current Oregon Residential Specialty Code. View more information on building codes

It is recommended that you visit the Development Services Center to talk with staff about your project while in the planning stages. Staff can help you determine if an ADU is allowed on your property and to discuss zoning standards that are applicable to your project. They can also help answer questions about the building code and applicable construction standards, and utilities.

There are a variety of design and use standards in the zoning code which apply to the creation of an ADU. These include limiting the overall number of residents in both units, limitation with respect to home occupations, and the location of entrance doors and size of the ADU. Where an ADU is created in a new detached structure there may be additional standards regulating the exterior appearance and materials of the ADU depending on the height of the ADU. These additional standards include provisions for the roof pitch, trim, eaves and windows.

When converting an existing unfinished space to an ADU, some features, such as ceiling heights, windows, stairs and insulation, may not meet current building code requirements for finished space. These conditions could make it expensive, difficult or even impossible for you to change your attic, basement or garage into living space.

The ADU Program Guide outlines zoning requirements, construction standards, utility standards and other requirements in detail.

Some research on your property may be required in preparation for submitting a building permit application. Find out how to research your property and where to locate the information in preparation for your permit application.

The following information must be submitted when applying for a permit to build an ADU. Since every project is unique, there may be some situations where you will be asked to provide additional information.

Site and building construction plans:For brand new construction, see the submittal standards and drawing criteria in the NSFR Intake Packet (see above). For altering an existing structure to add an ADU, see the submittal standards and drawing criteria in Adding a Dwelling Unit Submittal Requirements.

Erosion control plan (may be a part of the site plan) or completed simple site erosion control form, if the project will result in ground disturbing activity. Note: Erosion control measures shall be installed, inspected and approved even when a simple site erosion control form has been accepted.

Mitigation form and/or a stormwater plan if your project will add more than 500 square feet of impervious area

To submit for a permit, bring these forms, and four (4) copies of site, architectural, and structural plans (for the area of proposed work and areas affected by such work ) along with intake fees to the Development Services Center.

The Bureau of Development Services sells a "Residential Combination" permit package. This allows you to call for all inspections using just the Building Permit (RS) IVR number and pay for all the permits at one time. You will need to submit the trade (mechanical, electrical, and/or plumbing) application(s) signed either by you, if you are doing these portions of the work yourself, or by your licensed subcontractors. If you do not have your completed subcontractor forms when you are applying for your residential permit (RS) you will have to apply for trade permits separately from the building permit. Sub-contractors that you hire must be registered with the State of Oregon and carry the correct licenses in association with their trade.

Plan reviewers from the Bureau of Development Services representing fire life safety and structural disciplines, as well as staff from the Parks Bureau, Office of Transportation, Bureau of Environmental Services, and Water Bureau, will all participate in the review of your plans.

The bureaus/review groups that will check a typical conversion project include:

ChecksheetsA checksheet is sent to the applicant when a reviewer needs additional information or a correction has to be made to the plans. When you have gathered the additional information or made the corrections, bring the plans/information to the Development Services Center. Reviewers will be notified that a checksheet response has been received and the review will continue. More information on checksheets.

Status ReportsStatus reports are available after your project has been assigned to reviewers. Status reports show all reviews and include the reviewer’s name and phone number. To obtain a status report, call (503) 823-7000 and select option four to have a status report faxed to you or call (503) 823-7357 to have one mailed to you.

Permit IssuedWhen the last technical review is approved, your permit will be pre-issued. You will be contacted when your permit is ready, and of your final fee total. Fees may be paid by cash, check, Visa, MasterCard, American Express or Discover.

If your permit is ready for issuance, you may pick up your permit between 8:00 am - 3:00 pm, Monday-Friday (8:00 AM to Noon on Thursdays) at Permitting Services, located on the 2nd floor of1900 SW 4th Avenue, Portland, OR. For more information call (503) 823-7357.